1 | Materials
The core is made out of ABS plastic. There was two main reason for this: 1. I had experience with it. 2. You can easily form it under heat.
The outside padding is made out of low density EVA foam
The inside padding is is made out of a layer of insulation foam (because that's what I had at home and also was on roughly the size) and some random textile I've had laying around.
The outside and inside textile cover is made out of a strong workwear canvas. Again, because I had experience with it as it being strong and something that is good for painting on.
Leather straps and 3 buckle's for it.
Acrylic spray paint for the backside of the shield
2 | Construction
2.1 | The Core
Personally I used a 4,5mm thick ABS plastic (Acrylonitrile butadiene styrene) sheet as the core. The sheets I can buy here in Hungary I can make 3 shields, similar to what I'm describing here, but this may vary depending on what you can buy.
The core is basically a trapeze with the base line width 61cm (because that was the width of the sheet I bought) the height is 20 cm, top line's width is 55 or 50 cm depending on what shape you want, but you can use different numbers obviously. Keep in mind for the width that it will be much shorter because the raised middle part will be bent out of it. Basically you will lose at least 10 cm from the total width of the sheet before bending.
In my experience this material can be easily cut either with a hand saw or with a powertool. Though you have to keep in mind that if you do it too fast the saw will be full with half-molten plastic bits. Anyway, the rough shape can be easily cut out, no need to make it pretty at the first step. Then we have to mark the raised middle part.
basically the sides of the raised part should be around 5 cm